what does fopen do in c code example

Example 1: fopen function in c

#include<stdio.h>
#include<conio.h>
void main(){
  FILE *fp;
  //r means read file
  fp=fopen("sam.txt","r");
  fclose(fp);
  getch();
}

Example 2: c fopen

#include <stdio.h>
#include <stdlib.h>

int main () {
   FILE * fp;

   fp = fopen ("file.txt", "w+");
   fprintf(fp, "%s %s %s %d", "We", "are", "in", 2012);
   
   fclose(fp);
   
   return(0);
}